Patrick was born on January 13, 1966 in Lewiston, Maine, to Irish-American parents. He grew up in nearby Buckfield, Maine, graduating from Buckfield High School. While in high school, he placed third in a National Juggling Competition.

He made his acting debut in 1985 with a part in the movie Heaven Help Us. In 1987, he played a janitor, Rudy, in Meatballs 3. Shortly thereafter, he married actress and manager Rocky Parker, 27 years his senior. She had a son who was best friends with (and a year older than) Dempsey.

With Can't Buy Me Love, he achieved major movie star status in 1987. The "geek-to-popular" type comedy launched him and co-star Amanda Peterson to teen idol status, and in 1989, he turned in another strong performance in Loverboy, playing a pizza delivery guy.

But Dempsey's time in the limelight was short-lived, with his work during the 1990s consisting mostly of critically-panned box-office bombs, straight to video releases or TV movies. However, he did appear in the successful Mobsters (1991), JFK: Reckless Youth (1993) -- in which he played John F. Kennedy -- as well as With Honors (1994) and Outbreak (1995).

His luck turned around when he married his second wife, Jillian Fink, in 1999. Their daughter, Tallulah, was born in 2002. That same year, Dempsey played the fiancee of Reese Witherspoon in Sweet Home Alabama. He auditioned for the starring role in the popular series House, M.D. (which later went to Hugh Laurie) before landing the role of Dr. Shepherd on Grey's Anatomy. He's come full circle with show's popularity, and has gained new respect for fame.

The dyslexic Patrick has appeared in more than 40 films to date. He enjoys collecting antiques, remodeling homes and skiing in his spare time. He is co-owner of the Indycar Series team Vision Racing.